Chewing gums generally include gum base, water-soluble sweeteners and flavoring. The water-soluble sweeteners usually include sucrose, dextrose, corn syrup (in liquid form as a gum base plasticizer), and/or sorbitol liquid and/or sorbitol powder, or combinations thereof. The chewing gum is generally prepared by melting the gum base, mixing corn syrup or liquid sweetener for 3 to 5 minutes with the gum base followed by the addition of solid sweetener (for example, sugar) and flavor and mixing for 5 minutes. The chewing gum is removed from the kettle, rolled and cut to the desired shape.
In the above chewing gum, the corn syrup (which provides a substantial portion of the moisture in the gum) will be retained in the gum base as part of the oil or insoluble phase and the sucrose and/or other sweeteners will be incorporated in a water-soluble phase which is in simple admixture with the oil phase and might even be considered to be coated on the gum base. The result is that the gum base will protect the corn syrup as an internal phase thereby minimizing the amount of corn syrup on the surface of the gum (surface corn syrup causes the gum to sweat). However, due to the equilibrium relative humidity of the chewing gum, there is eventual migration of moisture from the corn syrup to the gum surface causing the gum base to be plasticized and the chewing gum to become soft and sticky so that it sticks to its wrapper. Futhermore, there is a subsequent loss of moisture through evaporation at the gum surface at equilibrium relative humidities below that of the gum. Reduction in moisture content of chewing gum leads to loss of flexibility which manifests itself in increased stiffness and brittleness. The latter phenomena is, of course, associated with stale or old chewing gum.
Thus, in summary, due to the moisture provided by liquid corn syrup, fresh chewing gum initially has a soft sticky consistency so that it tends to stick to its wrapper. After standing, for example, for several months, the chewing gum loses moisture as described above, becomes hard and less sticky and thus becomes stale. If the above sequence of events could be reversed so that fresh chewing gum has a relatively hard consistency and only after being wrapped becomes soft, the initial unwrapping problems and subsequent shelf-life problems could be very much alleviated.